CFRP Fastener Joint Assembly With Reflowed Conductive Gap Filler

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Solution Overview

Problem

Existing methods for managing electromagnetic energy (EME) conduction in carbon fiber reinforced plastic (CFRP) structures with metallic fasteners are inefficient and costly, leading to issues like hot particle ejection and thermal decomposition due to poor conduction between CFRP material and fasteners.

Innovation Solution

Applying a conductive gap filler or coating to the sidewalls of holes in CFRP structures and remelting it post-installation to ensure better EME conduction, or using sleeved fasteners with conductive coatings, to minimize voids and discontinuities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If metallic fasteners are used to secure CFRP structural elements, then mechanical strength and durability are improved, but electromagnetic energy conduction deteriorates due to gaps and rough surfaces in drilled holes

Engineering Contradiction:

Improvemechanical strengthVSAvoidEME conduction

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

A conductive gap filler material is introduced as an intermediary substance between the metallic fastener and the CFRP hole walls. This filler material fills the gaps and accommodates surface roughness, creating a continuous conductive pathway that bridges the electrical discontinuities caused by the mechanical connection

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrical conductivity parameter of the joint assembly is improved by changing the physical state and distribution of the conductive gap filler material. The filler material's conductivity properties are optimized to compensate for the poor EME conduction caused by gaps and rough surfaces in the drilled holes

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If drilled holes are created in CFRP for fastener installation, then mechanical fastening is achieved, but EME conduction deteriorates due to crevices and rough surfaces

Engineering Contradiction:

Improvefastener installationVSAvoidEME conduction

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The conductive gap filler serves as a mediator that compensates for the surface imperfections created by drilling. It fills the crevices and smooths over the rough hole walls, creating a continuous conductive interface without requiring additional manufacturing steps to improve hole surface quality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The conductive gap filler is applied to the hole walls before fastener installation, preparing the surface in advance to ensure good EME conduction. This preliminary action prevents the formation of conductive discontinuities rather than attempting to correct them after the fact

Inventive Principle:

Principle #10Preliminary action

3Productivity

If conventional fastening methods are used in CFRP, then structural assembly is achieved, but hot particle ejection occurs during lightning strikes due to poor EME conduction

Engineering Contradiction:

Improvestructural assemblyVSAvoidhot particle ejection

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The conductive gap filler material acts as a protective intermediary that ensures continuous EME conduction pathways during lightning strikes. By eliminating gaps and discontinuities, it prevents the concentration of electrical current that would otherwise cause thermal decomposition and hot particle ejection

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The conductive gap filler provides beforehand cushioning by pre-establishing continuous conductive pathways that protect against the harmful effects of lightning strikes. It cushions against current concentration and thermal spikes before they can cause hot particle ejection

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enhances EME conduction by reducing voids and discontinuities, thereby preventing hot particle ejection and improving structural integrity under lightning strikes.

Implementation Method 1

applying heat to the fastener and the conductive gap filler sufficient to melt and reflow the conductive gap filler

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 2

applying heat to the fastener sufficient to remelt and reflow the conductive coating

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentEP4684944A1Methods of increasing electromagnetic conduction within a structural joint assembly

Publication Date: 2026.01.28 THE BOEING CO

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AI summary

Methods of increasing electromagnetic energy conduction between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and structural elements, at least one of the structural elements formed as a layer of carbon fiber reinforced plastic. One method includes a) forming a first hole through a first structural element and a second hole through a second structural element, each of the holes being formed to align with the other; b) melting and applying a conductive gap filler to sidewalls of the holes; c) installing a shank portion of the fastener through the first and second holes to complete assembly; and d) after assembly, applying heat to the fastener and gap filler to remelt and reflow the conductive gap filler. Another method involves applying a conductive coating to the shank portion in lieu of applying conductive gap filler to sidewalls of the holes.